linux-kernel - [PATCHv3] Make for_each_cpu

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Date:	Tue, 13 May 2008 11:28:21 +0200
From:	Alexander van Heukelum <heukelum@...lshack.com>
To:	Andreas Schwab <schwab@...e.de>
Cc:	Mike Travis <travis@....com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Jackson <pj@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Matthew Wilcox <matthew@....cx>,
	ARCH <linux-arch@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexander van Heukelum <heukelum@...tmail.fm>
Subject: [PATCHv3] Make for_each_cpu_mask a bit smaller

The for_each_cpu_mask loop is used quite often in the kernel. It
makes use of two functions: first_cpu and next_cpu. This patch
changes for_each_cpu_mask to use only the latter. Because next_cpu
finds the next eligible cpu _after_ the given one, the iteration
variable has to be initialized to -1 and next_cpu has to be
called with this value before the first iteration. An x86_64
defconfig kernel (from sched/latest) is about 2500 bytes smaller
with this patch applied:

   text	   data	    bss	    dec	    hex	filename
6222517	 917952	 749932	7890401	 7865e1	vmlinux.orig
6219922	 917952	 749932	7887806	 785bbe	vmlinux

The same size reduction is seen for defconfig+MAXSMP

   text	   data	    bss	    dec	    hex	filename
6241772	2563968	1492716	10298456	 9d2458	vmlinux.orig
6239211	2563968	1492716	10295895	 9d1a57	vmlinux

Signed-off-by: Alexander van Heukelum <heukelum@...tmail.fm>

---

On Mon, May 12, 2008, Andreas Schwab wrote:
> > +#define for_each_cpu_mask(cpu, mask)			\
> > +	for ((cpu) = ~((typeof(cpu))0);			\
> 
> There is no need for such a complicated expression, -1 will work for
> every (arithmetic) type.

Indeed, thanks.

This version applies on top of sched/latest.

This version reuses the already-existing api next_cpu instead
of inventing a new one; initializing the iteration counter to
-1 was suggested by Matthew Wilcox. Now with a -1 instead of
an overly carefull ~((typeof(cpu))0). "-1" is properly sign-
extended even if cpu is u64 in a 32-bit environment.

Greetings,
	Alexander

 include/linux/cpumask.h |   16 ++++++++--------
 1 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 73434e5..c24a556 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -377,10 +377,10 @@ int __any_online_cpu(const cpumask_t *mask);
 #define first_cpu(src)		__first_cpu(&(src))
 #define next_cpu(n, src)	__next_cpu((n), &(src))
 #define any_online_cpu(mask) __any_online_cpu(&(mask))
-#define for_each_cpu_mask(cpu, mask)		\
-	for ((cpu) = first_cpu(mask);		\
-		(cpu) < NR_CPUS;		\
-		(cpu) = next_cpu((cpu), (mask)))
+#define for_each_cpu_mask(cpu, mask)			\
+	for ((cpu) = -1;				\
+		(cpu) = next_cpu((cpu), (mask)),	\
+		(cpu) < NR_CPUS; )
 #endif
 
 #if NR_CPUS <= 64
@@ -394,10 +394,10 @@ int __any_online_cpu(const cpumask_t *mask);
 int __next_cpu_nr(int n, const cpumask_t *srcp);
 #define next_cpu_nr(n, src)	__next_cpu_nr((n), &(src))
 #define cpus_weight_nr(cpumask)	__cpus_weight(&(cpumask), nr_cpu_ids)
-#define for_each_cpu_mask_nr(cpu, mask)		\
-	for ((cpu) = first_cpu(mask);		\
-		(cpu) < nr_cpu_ids;		\
-		(cpu) = next_cpu_nr((cpu), (mask)))
+#define for_each_cpu_mask_nr(cpu, mask)			\
+	for ((cpu) = -1;				\
+		(cpu) = next_cpu_nr((cpu), (mask)),	\
+		(cpu) < nr_cpu_ids; )
 
 #endif /* NR_CPUS > 64 */
 
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